HDTV as PC Monitor / Why 1080i ?

1 reply [Last post]
Joined: Dec 19 2005

Do you need a PC monitor if you own a HDTV (assuming your PC is in the livingroom)?
1920x1080 seems good enough as most PC users are stuck with 1280x1024 or even lower res.

HD(V) signals are stored as 1440 anamorphic pixels or 1280 square pixels.
Are there 1440 anamorphic pixels or 1920 square pixels on a HDTV line ?

I know that interlaced video delivers better motion than progressive but it seems to me that all
HDTV's are flat TFT/LCD/plasma devices. Aren't flatpanel screens always progressive scan ?
Then why care about 1080i if it's gonna be de-interlaced anyway?
Or are there interlaced/CRT HDTV's out there ?

Alan Roberts
Alan Roberts's picture
Joined: May 3 1999

HDTV has two official resolutions, 1280x720 progressive and 1920x1080 interkaced or psf (progressive with segmented frames, like film). Programme material comes from a variety of sources, expensive stuff (like Dalsa Origin, Arri D20, Panavision Genesis, Thomson LDK6000 or Viper or Sony HDC950 recorded on HD-D5 or HDCAM-SR or hard drives) records full resolution, medium stuff (like HDCAM (900 or 750 or 730 or 730s) or DVCProHD (e.g. Pansconic 20A or Varicam)) lower the horizontal resolution to 1440 for 1080, 960 for 720. Cheap stuff (HDV) record these lower resolutions but also reduce the vertical chroma resolution by 50%. And it shows.

When all these standards were formalised, the only sensible displays were either big, expensive crts or big projectors. Since then though, plasma and lcd displays have improved dramatically, so that they njow dominate the large- and medium-size display markets. As you say, these are all progressive devices so involve de-interlacers, but they alos have scalers since few of them actually have pixel numbers that match the pictures, and even fewer of the dispense with overscan.

So, pretty well all the displays you're likely to use for HDTV will be pixel-based, crts are on the way out. There are still interlaced lcds out there though, but they interlace at their own resolution, not at that of the signal. All the broadcasters want to migrate to progressive signals eventually, but not at the price of lower resolution. So, we are going to see a migration in the standards, with 720p and 1080i coexisting until 1080p happens. That'll take a few years because the data rates are so high. In the meantime, mucyh of the 1080i production is actually 1080psf (film, drama, documentary, etc) so the signals are already progressive. It's only sports, news and music that's likely to stay with interlaced 1080, because they want the smooth motion and higher resolution.

Hope that helps.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.